A liquid crystal display (LCD) includes a liquid crystal alignment film. The liquid crystal alignment film is mainly made of polymer materials. The liquid crystal alignment film directs the alignment of liquid crystal molecules. When the liquid crystal molecules are moved by the influence of an electric field to display an image, the liquid crystal alignment film allows the liquid crystal molecules to be oriented in a predetermined direction. Generally, it is necessary to uniformly align the liquid crystal molecules in order to provide uniform luminance and a high contrast ratio to the liquid crystal device.
The conventional method of aligning liquid crystal molecules includes coating a polymer film such as a polyimide on a substrate made of a material such as glass, and rubbing the surface of the substrate with a fiber such as nylon or polyester in a certain direction. However, the rubbing method may cause serious problems when fabricating a liquid crystal panel due to fine dust or electrostatic discharge (ESD) that may be generated while rubbing the polymer film with the fiber.
In order to solve the problems of the rubbing method, a photo-radiation method has recently been researched to induce anisotropy to the polymer film by irradiating light on the membrane so as to align the liquid crystal molecules.
As polymer film materials for the photo-alignment method, polymers having photo-functional groups such as azobenzene, cumarine, chalcone, and cinnamate have been suggested. To prepare the polymers with photo-functional groups, dinitro-based compounds with excellent stability should be used. However, the dinitro-based compounds include double bonds which can degrade where photo-crosslinking occurs due to polarized photo-radiation in the course of preparing the polymers with photo-functional groups. Thus, it is difficult to use the dinitro-based compounds to prepare a photo-alignment agent. Also, the process for preparing the polymers with photo-functional groups is too complicated to be economically efficient.